Perq 2T1 display fault

From: Jules Richardson <julesrichardsonuk_at_yahoo.co.uk>
Date: Sat Feb 21 03:36:48 2004

On Sat, 2004-02-21 at 03:48, Tony Duell wrote:
> > So, the 2T1 has a standard KME as you say - it looks to have correct
> > horizontal and vertical drive, with the exception that it skips every
> > few lines, leaving a blank horizontal gap. I can see what look to be
>
> That does _not_ sound like a monitor problem. You're getting missing
> video every few scan lines, right? In which case, either you've got some
> Analogue signal that's blanking the display _and_ which is locked to the
> vertcial sync signal, or you've got a problem with the memory board
> (middle board in the cardcage) in the PERQ.

Ahh, fair call - I was wondering along the lines of bad cap or otherwise
in the vertical drive, such that it was the display itself which was
producing uneven deflection (because I can only see vague character
shapes I can't tell if I'm actually missing data, or if there are blank
lines effectively inserted into the display by the monitor itself)

I am not a display expect by any means! :)

> How far does it get through the self-tests? What's the final number on
> the DDS display (front of the CPU box) when it tries to boot?

It gets to 999, which I assumed was normal - but maybe not! Maybe the
character data on the screen is telling me there's a video problem, but
that isn't much use if there's a video problem ;)
 
> The display has an unstable shimmering
> > right margin to it, which definitely looks analogue in nature.
>
> That may be normal. There's some marginal timing in the vidro circuitry,
> and often the right few pixels are a bit unstable :-( At least one of my
> PERQs does that...

Ahh, ok.

> > Ahh, yes it will be. I checked all the connectors and reseated the
> > boards plus chips - I remember seeing a few socketed ones that didn't
> > look like they would have originally been socketed.
>
> You'd be suprised. The only chips I _remember_ socketting was an op-amp
> on the hard disk analogue PCB.

Fair enough :) I love the dual-stacking of chips on the memory board!

cheers

Jules
Received on Sat Feb 21 2004 - 03:36:48 GMT